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Genetics: How genes make us who we are
• Genetics is the study of heredity• Heredity is the passing of traits from one
generation to the next• YOUR biological inheritance is the unique
blend of genes that are passed to you by your parents
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II. Mendel- The Father of Genetics
• Gregor Mendel– Lived 150 years ago– Austrian monk– Good at Math– Taught high school– Grew pea plants – Careful and persistant
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Mendel’s Model Organism – the Garden Pea
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Mendel noticed that the peaPlants in his garden differed.He noticed 7 differences or traits which he decided to study.
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Genetics Vocabulary to Know
• Trait – Inherited feature or characteristic: examples are eye
color, pea plant height• Allele
– One form of a trait. Example eye color: blue eyes or brown eyes
• Genotype– What the genes say Hh or HH or hh
• Phenotype– Outward appearance: having blue eyes
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Mendel asked how are these traits inherited
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IV. Mendel’s 1st Experiment• He mated tall x short plants and got all tall• What happened to the short plants, why did’nt the
two parents traits BLEND in the offspring??????
PP
FF11
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V. Mendel’s 2nd Experiment• QUESTION: What happened to the short plants???• 2nd EXPERIMENT: Mendel allowed both the tall plants and the
short plants to self-pollinate• RESULTS: NOW the short plants ‘come back’, they can be seen
in the next generation BUT only ¼ plants are short
FF11
FF22
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Characters investigated by Mendel
Mendel repeated this experimentWith 7 more pea plant traits
The results were always thesame
No matter which trait Mendellooked at he saw the 3:1 ratio in the off spring
He drew 3 conclusions from theseexperiments. Today we under-stand the molecular basis of Mendel’s findings.
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Monohybrid Crosses Yielded Consistent Results
Therefore, the Principle of Segregation indeed is a general principle of genetics.
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Mendel’s CONCLUSIONS from his experiments
Traits are inherited by some factor (which we now call genes) being passed from parent to offspring
There are different forms of each factor (gene) that produce the traits, these are alleles. Some alleles are dominant and some are recessive, the recessive will only show if the dominant is not present.
Each parent organism must not be giving BOTH of it’s alleles, they are separating and passing on only ONE to the offspring
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Here is Mendel’s first experiment again with seed color instead of tall vs short
Imagine we can look inside the plant at the genes, the genotype, as well as see the outside, the phenotype
The genes for yellow color are YYThe genes for green color are yyYellow(Y) is dominant to green(y)
A Punnet square is used to show the possible results of the mating or cross
P generation is the parents
F1 is the first generation of children
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Staying the Course – Mendel Continued Crosses to the F2 (the grandchildren)
What was learned?
The green trait was not lost or altered, even though it disappeared in the F1.
One trait is dominant to the other in its expression.
The reappearance of the recessive trait in ¼ of the F2, suggests genes come in pairs that separate in the formation of sex cells.
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NOW 150 years later!!! we know more about Genes, Alleles, and Chromosomes:So this is what is happening inside the chromosome…
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VI. More terms
Homozygous – a parent that has two identical alleles for a gene (ex: TT, tt, AA, aa)
Heterozygous – a parent that has two different alleles for a gene (ex: Tt, Aa)
Recessive – form of a trait which does not appear if in the presence of the other form, blue eyes
Dominant – form of the trait which is seen even if both alleles are present, example brown eyes